Cook chicken with small
amount of celery and onion in water to cover.Chill and slice thin.Remove
most of the fat from chicken broth, reserve broth.Cook broken-up spaghetti, rinse.Make sauce: Brown butter; stir in flour.Add chicken broth, stirring to make thick sauce.Add Worcestershire sauce, half of the cheese
and the mushrooms.Cook until
thickened.Add salt and pepper to
taste.In a 9 x 13 x 2 inch baking
dish, layer spaghetti, chicken and remaining cheese.Pour sauce over.Bake at
350° for 15 minutes.